The active or passive penetration of pathogens into a host, the inherent presence of these therein and the propagation thereof is referred to as infection. Sources of infectious particles occur everywhere. For example, the human body is colonized by a large number of microorganisms which are generally kept under control by the normal metabolism and an intact immune system. However, a weakened immune system, for example, may result in significant propagation of the pathogens and, according to the type of pathogen, in different disease symptoms. For many pathogen-induced diseases, medicine has specific antidotes at its disposal, for example antibiotics against bacteria or antimycotics against fungi or virustatics against viruses. However, increasing occurrence of resistant pathogens is observed when these antidotes are used, and some of these pathogens have resistances against several antidotes at the same time. The occurrence of these resistant or multiresistant pathogens has made the treatment of infection disorders increasingly difficult. The clinical consequence of resistance is manifested by a failure of the treatment, particularly in the case of immunosuppressed patients.
New starting points for control of resistant or multiresistant disease pathogens are therefore firstly the search for new antidotes, for example antibiotics or antimycotics, and secondly the search for alternative means of inactivation.
An alternative method which has been found to be useful is the photodynamic inactivation of microorganisms. Two different photooxidative processes play a crucial role in the photodynamic inactivation of microorganisms. Prerequisites for the running of a photooxidative inactivation are firstly the presence of a sufficient amount of oxygen and secondly the localization of a so-called photosensitizer, which is excited by light of an appropriate wavelength. The excited photosensitizer can bring about the formation of reactive oxygen species (ROS), which can form firstly free radicals, for example superoxide anions, hydrogen peroxide or hydroxyl radicals, and/or secondly excited molecular oxygen, for example singlet oxygen.
For both reactions, the photooxidation of specific biomolecules directly adjacent to the reactive oxygen species (ROS) is of primary importance. This involves particularly oxidation of lipids and proteins which occur, for example, as constituents of the cell membrane of microorganisms. The destruction of the cell membrane in turn results in inactivation of the microorganisms in question. For viruses and fungi, a similar elimination process is assumed.
For example, singlet oxygen attacks all molecules. However, unsaturated fatty acids in the membranes of bacteria are particularly prone to damage. Healthy endogenous cells have a cellular defence against attacks by free radicals, called catalases or superoxide dismutases. Therefore, healthy endogenous cells can counteract damage by reactive oxygen species (ROS), for example free radicals or singlet oxygen.
The prior art discloses numerous photosensitizers which come, for example, from the group of the porphyrins and derivatives thereof or phthalocyanines and derivatives thereof or fullerenes and derivatives thereof or derivatives of the phenothiazinium structure, for example methylene blue or toluidine blue, or representatives of the phenoxazinium series, for example Nile blue. The photodynamics of methylene blue or toluidine blue with respect to bacteria have already been used, for example, in dentistry.
The photosensitizers known from the prior art are usually substances having a relatively complex molecular structure and therefore complex purification processes.
The non-patent literature Svoboda et al. (Chem. Eur. J. 2008, 14, pages 1854-1864) describes the influence of thiourea on the photooxidation of benzyl alcohol by flavin and various flavin derivatives, including the compound having the formula (20):

However, Svoboda et al. do not describe any effect of the flavin derivatives examined on the viability of microorganisms.
It is additionally known that 10-methyl-10H-benzo[g]pteridine-2,4-dione derivatives riboflavin and tetraacetylriboflavin have high yields of singlet oxygen, although the affinity for microorganisms is low. It is additionally known that singlet oxygen can diffuse only over a short distance before it reacts or is degraded. Therefore, the inactivation of microorganisms by 10-methyl-10H-benzo[g]pteridine-2,4-dione derivatives riboflavin and tetraacetylriboflavin is inadequate.
Moreover, WO 2010/019208 A1 and WO 2011/008247 A1 disclose numerous flavin, roseoflavin and riboflavin derivatives which can bind to flavin mononucleotide (FMN) riboswitches. Riboswitches are RNA elements in the untranslated regions of the mRNA of prokaryotes, fungi and plants, which bind low molecular weight metabolites, for example FMN, and then regulate gene expression. For example, after binding of FMN to FMN riboswitches of prokaryotes, the expression of enzymes responsible for riboflavin and FMN biosynthesis is repressed, as a result of which riboflavin and FMN biosynthesis stops. Riboflavin assumes a central role in the metabolism, since it serves as a precursor for flavin coenzymes. Therefore, suppressed riboflavin and FMN biosynthesis leads to reduced viability.
However, this form of control of pathogenic microorganisms can likewise result in occurrence of resistances, which can arise, for example, as a result of mutations in the RNA elements in question.